Now i've got my K100LT back up and running again it's time to think about new rubber.

But i'm confused about what to go for.

I've trawled through old posts and come up with so many options but none that answer my questions so here goes.

My K has a 140 on the rear when it was shipped with a 130 from new.

What sizes should i be fitting to the front and back and what effect will it have on the handling?  Why fit bigger?  The 140 is very close to the swingarm with less than a 1cm gap.

Also where i live nobody who will fit tyres will mix them up so i have to go for a matched set.  I don't push my K that hard but i will be using it almsot everyday and in all weathers.  So i need high milleage with good grip in the wet.

Any ideas please as i want to get them fitted maybe this weekend and i'll need to order them soon.

Mike

I put on BT45 and they are great in the wet. I don't know about mileage, but there was a set on the LT when I got it and they lasted well. My priority is always good in wet and mileage a long way behind.

G'day Mike , most here with stock rims run 110/80/18 front with a 140/& 80/17 rear , these are plus 1 over the stock 100/90/18 + 130/90/17 , handling should be quite neutral , all things considered , as far as brand is concerned I'm sure other will chime in

good luck with it

JR

The majority of Ks started with 100/90 front and 130/90 rear(K75c excepted).  At that stage all tyres available for the K were crossplies.

When radial tyres for motorcycles were introduced, BMW introduced them on one of the special edition K100RS's  by fitting that bike with 110/80 front and 140/80 rear radial tyres (Michelin i think maybe).  The rims are the same size.  The standard RS of the time still had the 100/90 and 130/90 combo.

You can fit either, it's a personal choice. Seem to be stickier/sportier tyre choices available in the wider size.

Al

Does changing the rear tyre size affect the speedo at all?

Mike

Mike101 wrote:Does changing the rear tyre size affect the speedo at all?

Mike

140/80 looses about 5mm on the radius of the wheel compared to 130/90 so will register higher than actual speed

Your speedo will read marginal higher with the 140/80 but not that I would be concerned, Around 1.5 - 2mph at 60mph.

Try Pirelli Demon Sport. Bias-belted but very nearly as good as a radial.

I put on the sport demons on the RT last year. It was a big improvment  on wet roads.
So far over 1500 mi. still a lot of tire left. Handling feels very good.

From my investigations, the two main contenders are the Pirelli Sport Demons or the Bridgestone BT45.  From what I've read you can't go wrong with either.

Haven't used the Pirelli, but never had a problem with the Bridgestones.

If you check most tyre brand web sites they have a tyre ref page, you use the drop down box to select your bike and it will give you the tyres to fit, the above work and the only one not mentioned are the dunlop d404's which come as a matched set, cant say anyone in here have used them of late.

Stock sizes - bias ply: Bridgestone Spitfires

Radial (if your installer requires "matched" F&R tires): Avon AV45 110/80-18, AV46 140/80-17

I've already done a review of skinny radials, perhaps I need to do another for bias plys.

Radials are not recommended for the Y-spoke rims, so sticking with matched sets of bias-ply's, I can personally recommend Bridgestone (110 BT45 front and 130 Spitfire rear) or a set of Metzler's (100 front and 120 rear). 

I have plenty of notes on various other brands, but it's hard to get information on matched sets. It seems most people people start out with matched sets, but end up replacing the rear tire and viola'--mis-matched sets. 

The most important thing to focus on first is a rear tire. Once you decide on that, it's a simple matter to match up the front. A 130 on the rear is fairly standard, and a good place to start. I've seen bias ply 140s on the rear too, and if you are so inclined there's a wider spacer to help with swing-arm clearance. 

In selecting a front tire you can go with either 100 or 110. If you can't find what you want in a 110, a 100 will still do nicely. Some people have said they prefer 100's over 110s in high speed cornering. I know that's not an issue here, but just repeating what I've read to illustrate the point that there's no need to go with a wider tire up front.

Other brands to consider (recommended at various times on this site) are Dunlop, Continential, Michelin, Avon, Pirelli, and Kenda.

Mike101 wrote:

Any ideas please as i want to get them fitted maybe this weekend and i'll need to order them soon.

Mike

At the risk of repeating myself, as well intentioned as the advice is from members all over the globe, it is worth considering that what works well in their location may not be so good where you ride. There are many things that vary; road surface construction and repair, weather, even the type of road marking materials.

I can't see why not to run radials on Y-spokes.  The tire doesn't know or care how many spokes the wheel has.

Not sure what kind of surfaces you ride but some areas of the US groove freeway to improve rain drainage and reduce hydroplaning.  A front tire with a straight groove down the middle will track on these grooves. It's not dangerous but it sure is annoying.

Example: Michelin Mac50:

good words mike

Am I the only one that buys whatever is on special ?

Hmmm , dunno RobinW , for me there are probably three things that I wouldn't muck with on my bike , I get the best I can afford for : brakes , oils and tyres , considering how little rubber is keeping you in touch with terra firma I'd say it's unwise , others may wish to differ

JR

duck wrote:I can't see why not to run radials on Y-spokes.

A while back someone wrote about the differences between the original Y-spoke and the later modified version. The original has a concave outer ring welded to the rim, and I haven't seen the modified version, but am told it is flat.

The outer ring is probably the reason BMW doesn't recommend radials for Y-spoke rims. Radials transfer a lot of energy to the sidewalls, putting extra pressure on this outer ring. Looking at the ring it becomes clear that over time the welds may crack under the added pressure of radial tires. One could surely get away with it in the short term, but give the multitude of road conditions one encounters, year-after-year, the likelihood of damaging the rim on radials seems certain.

Back to the original question; Mike101--just put on a set of Metzler's. They are a good all-round tire and designed especially for BMWs. These are a bit more expensive (here at least), but will give good performance and longevity. For your bike a 130 rear and 100 front will provide excellent stability and cornering.

Enjoy the ride.  

I went straight from sidewall cracked old 100/90-18 and 130/90-17 tyres to the plus-one sizes, 110/80-18 and 140/80-17, when I was using Y spoke wheels on my RS, with absolutely no ill-handling or clearance issues whatsoever. I do prefer Pirelli's incredible, radial-like, but bias, Sport Demon tyres for their handling and relatively good tread life, but Bridgies BT45, Michies Pilot Activ (upgraded Macadam) and a few others, work well too.

Duck's concept of a radial BT023 Bridgie and an Avon radial out back is worth considering, but I'm squeamish about mixing brands. The Japanese tyre engineer probably didn't stay up late drinking sake with the Pommie tyre engineer to be sure their tyres work in conjunction with the other brand. We take a lot of chances when we ride, so it comes down to how it personally feels, whether you remain confident about what those relatively thin strips of rubber and silica are doing, making contact with the bitumen under you as you roll.

The AV46 "plays well together" with either a BT-023 or a Pilot Road 2 front. (In case you prefer a front tire that stays out late drinking fancy wine and chasing skirts.)

Well around me all i can get fitted are the BT45's or sport demons.

Nobody will mix brands and nothing else is stocked.

Mike

Well Mike, you're in luck so   

Both of those are ideal for the K.

If you can't decide which one - look (waste a few hours) on the net.  If that doesn't help you make up your mind, flip a coin.

Based on what I read, both will do a good job, and give good mileage.

As regards size, 100/110 or 130/140 - I wouldn't worry on the LT. I'd go for which ever one they had in stock, and if they have both sets, whichever tyre is newer (you can get the manuf. date from the sidewall - have a google if you don't know how).

On saying that, I'd stick with a 100 front and a 130 rear,  or a 110 front and a 140 rear.

Well, it sounds like your choices have been limited for you.  In this case, whichever has the lower price or is in stock should be your deciding factor.

I wouldn't agonize over it.  Both the Sport Demon and BT045 are good tires.

AJ.Valente wrote:

duck wrote:I can't see why not to run radials on Y-spokes.

A while back someone wrote about the differences between the original Y-spoke and the later modified version. The original has a concave outer ring welded to the rim, and I haven't seen the modified version, but am told it is flat.

The outer ring is probably the reason BMW doesn't recommend radials for Y-spoke rims. Radials transfer a lot of energy to the sidewalls, putting extra pressure on this outer ring. Looking at the ring it becomes clear that over time the welds may crack under the added pressure of radial tires. One could surely get away with it in the short term, but give the multitude of road conditions one encounters, year-after-year, the likelihood of damaging the rim on radials seems certain.

Back to the original question; Mike101--just put on a set of Metzler's. They are a good all-round tire and designed especially for BMWs. These are a bit more expensive (here at least), but will give good performance and longevity. For your bike a 130 rear and 100 front will provide excellent stability and cornering.

Enjoy the ride.  

BMW doesn't recommend radials on a vintage K bike because of liability issues.  The excuses I've heard are rim design and the suspension isn't designed for radials.  I asked them to explain to me what difference there would be in the suspension when the forks, springs and rear shock all can be used on other motor cycles that can run radials.  Their response to me was  that it's technical, you wouldn't understand.  In the U.S. that's legal talk for we don't want to be held liable.

AJ.Valente wrote:

duck wrote:I can't see why not to run radials on Y-spokes.

A while back someone wrote about the differences between the original Y-spoke and the later modified version. The original has a concave outer ring welded to the rim, and I haven't seen the modified version, but am told it is flat.

The outer ring is probably the reason BMW doesn't recommend radials for Y-spoke rims. Radials transfer a lot of energy to the sidewalls, putting extra pressure on this outer ring. Looking at the ring it becomes clear that over time the welds may crack under the added pressure of radial tires. One could surely get away with it in the short term, but give the multitude of road conditions one encounters, year-after-year, the likelihood of damaging the rim on radials seems certain.

Back to the original question; Mike101--just put on a set of Metzler's. They are a good all-round tire and designed especially for BMWs. These are a bit more expensive (here at least), but will give good performance and longevity. For your bike a 130 rear and 100 front will provide excellent stability and cornering.

Enjoy the ride.  

This makes no sense. The wheels are CAST so there's no weld to crack.

AJ.Valente wrote:

duck wrote:I can't see why not to run radials on Y-spokes.

A while back someone wrote about the differences between the original Y-spoke and the later modified version. The original has a concave outer ring welded to the rim, and I haven't seen the modified version, but am told it is flat.

The outer ring is probably the reason BMW doesn't recommend radials for Y-spoke rims. Radials transfer a lot of energy to the sidewalls, putting extra pressure on this outer ring. Looking at the ring it becomes clear that over time the welds may crack under the added pressure of radial tires. One could surely get away with it in the short term, but give the multitude of road conditions one encounters, year-after-year, the likelihood of damaging the rim on radials seems certain.

Back to the original question; Mike101--just put on a set of Metzler's. They are a good all-round tire and designed especially for BMWs. These are a bit more expensive (here at least), but will give good performance and longevity. For your bike a 130 rear and 100 front will provide excellent stability and cornering.

Enjoy the ride.  

The limited production sport models of the RS from -86 to -89 did all have
y-spoke rims and Pirelli radials fitted from factory.

The reinforced y-spoke with flat sidewalls came late -88.

duck wrote:

AJ.Valente wrote:

duck wrote:I can't see why not to run radials on Y-spokes.

A while back someone wrote about the differences between the original Y-spoke and the later modified version. The original has a concave outer ring welded to the rim, and I haven't seen the modified version, but am told it is flat.

The outer ring is probably the reason BMW doesn't recommend radials for Y-spoke rims. Radials transfer a lot of energy to the sidewalls, putting extra pressure on this outer ring. Looking at the ring it becomes clear that over time the welds may crack under the added pressure of radial tires. One could surely get away with it in the short term, but give the multitude of road conditions one encounters, year-after-year, the likelihood of damaging the rim on radials seems certain.

Back to the original question; Mike101--just put on a set of Metzler's. They are a good all-round tire and designed especially for BMWs. These are a bit more expensive (here at least), but will give good performance and longevity. For your bike a 130 rear and 100 front will provide excellent stability and cornering.

Enjoy the ride.  

This makes no sense. The wheels are CAST so there's no weld to crack.

+10

JR_K100RS wrote:Hmmm , dunno RobinW , for me there are probably three things that I wouldn't muck with on my bike , I get the best I can afford for : brakes , oils and tyres , considering how little rubber is keeping you in touch with terra firma I'd say it's unwise , others may wish to differ

JR

So you would stick with xxx even though yyy is 25% cheaper. I recently went to get a set of angels on a bike, they said on the phone they had em. When I got there it was the old 18" excuse, oh I thought it was 17". It's xmas, they won't courier over xmas, how about dunlops for $50 less. I mean, they aren't going to kill you, they'd get sued.

I get my tyres from http://www.rockymountainatvmc.com/d/12/Motorcycle-Tires heaps cheaper than Oz including freight and takes 4-5 days to deliver.

How do you balance the wheel?  Do you fit them yourself?

I have a guy here that fits them and balances the rear one dynamically and the front I balance myself.
Last time he charged me $13 to do both ends.

IngeK wrote "The limited production sport models of the RS from -86 to -89 did all have y-spoke rims and Pirelli radials fitted from factory. The reinforced y-spoke with flat sidewalls came late -88."

OK, so they recast the Y-spoke rims after a limited production run, humm.  Why'd they do that? Perhaps they found cracking on the edges of the rim?

So, are the flat sidewall Y-spokes OK for radial tires-is that the conclusion here? 

Wouldn't there be a service advisory on the subject from BMW?

The change in rims came midway through the production run on the sports model so both types of rim were used for the radial tyres.
From my knowledge of rims and tyres for motorcycles there is no difference in the rim requirements for radial or cross/bias ply tyres.  However it is advisable that appropriate tyre sizes are used for the rim being used. This is far more important for the Bias ply tyres than Radial construction tyres.

the flat sided rims may have coincided the release of the k1 and later
I have a suspicion that it looked different and they wanted to highlight the design changes as they went onto the 16 valve k100 models et al ... also about the same time they started using the 12 rivett output shafts, paralever rear etc
or so im lead to believe
the grooved rims seems appropriate for all the models that used them  so its more like a generational change ?

I understood that the rim change coincided with a change in the alloy owing to rim damage claims.

Having restored both types I can say that the later version does seem to be a slightly harder alloy.

The first batch of K75RTPs we had delivered, had the flat sided rims and came with Dunlop radials from BMW. The tyres weren't a success, not because they were no good but because the front tyre profile was a bit like a Toblerone, very tall in the centre. Once the front had a few hundred miles on it it was okay but when new, at high speeds, the wobble and weave was pretty unpleasant to say the least.

RobinW wrote:

JR_K100RS wrote:Hmmm , dunno RobinW , for me there are probably three things that I wouldn't muck with on my bike , I get the best I can afford for : brakes , oils and tyres , considering how little rubber is keeping you in touch with terra firma I'd say it's unwise , others may wish to differ

JR

So you would stick with xxx even though yyy is 25% cheaper. I recently went to get a set of angels on a bike, they said on the phone they had em. When I got there it was the old 18" excuse, oh I thought it was 17". It's xmas, they won't courier over xmas, how about dunlops for $50 less. I mean, they aren't going to kill you, they'd get sued.

Yep, same here.  I'd rather get what I want than what the shop has even if it's cheaper.  I stuck to my guns and got the Angel GTs (even after Pirelli initially delivered a rear 17 instead of an 18, Pirellis fault; the packing slip said 18, the tyre wall 17) and they are worth it.

When I've got stuck and had to accept what was on the shelf because it was my only choice I've invariably ended up with a bike that handled worse for it. Re Dunlops I've had good and bad, good were the D207s on my VTR, truly horrible were the new D220s that came on my TDM, once the rear was worn out I chucked the half worn front too.  The bike became much more enjoyable to ride after fitting new Michelins or Bridgestones or whatever they were.  I tend to stick to Michelin, Pirelli or Metzeler on my road bikes, Bridgestone are OK but don't seem to get the miles out of them.  The sidecar gets car tyres all round, the Super Ten runs Mitas or Heidenau because none of the mainstream brands make a 50/50 tyre (only 90/10 almost roadies or full knobs)


Al

MikeP wrote:the front tyre profile was a bit like a Toblerone

Sig line material. LOL.

To put it into a timeline: 16V models, (K1, K100-16) came with three spoke wheels not Y spoke so never an issue that a radial wasn't gunna be ridden on those. The 12 rivet outputs are circa 1986, too early for 'common' radials and no three spoke wheels yet in sight.

But BMW themeselves still did fit radials to the Y-spoke wheels in production.

Al

AL-58 wrote:But BMW themeselves still did fit radials to the Y-spoke wheels in production.

Al

There's not a question or doubt that they didn't, in my statement. I remember well the radials on the Y spoke wheels of the K100RS.

Introduced in Feb of '86, the K100 RS “Motor sports” with radial tyres of 100/90 VR 18 and 140/80 VR17, fork stabilizer (from K75), black windscreen, footrest plates and Y spoke wheels. Paint was Perlmutt White. The edition was limited to 1,000 bikes.

A useful link: http://www.k100.biz/pdf/K100_dati_produzione.pdf

AL-58 wrote:

RobinW wrote:

JR_K100RS wrote:Hmmm , dunno RobinW , for me there are probably three things that I wouldn't muck with on my bike , I get the best I can afford for : brakes , oils and tyres , considering how little rubber is keeping you in touch with terra firma I'd say it's unwise , others may wish to differ

JR

So you would stick with xxx even though yyy is 25% cheaper. I recently went to get a set of angels on a bike, they said on the phone they had em. When I got there it was the old 18" excuse, oh I thought it was 17". It's xmas, they won't courier over xmas, how about dunlops for $50 less. I mean, they aren't going to kill you, they'd get sued.

Yep, same here.  I'd rather get what I want than what the shop has even if it's cheaper.  I stuck to my guns and got the Angel GTs (even after Pirelli initially delivered a rear 17 instead of an 18, Pirellis fault; the packing slip said 18, the tyre wall 17) and they are worth it.

When I've got stuck and had to accept what was on the shelf because it was my only choice I've invariably ended up with a bike that handled worse for it. Re Dunlops I've had good and bad, good were the D207s on my VTR, truly horrible were the new D220s that came on my TDM, once the rear was worn out I chucked the half worn front too.  The bike became much more enjoyable to ride after fitting new Michelins or Bridgestones or whatever they were.  I tend to stick to Michelin, Pirelli or Metzeler on my road bikes, Bridgestone are OK but don't seem to get the miles out of them.  The sidecar gets car tyres all round, the Super Ten runs Mitas or Heidenau because none of the mainstream brands make a 50/50 tyre (only 90/10 almost roadies or full knobs)


Al

Yup , X2 on your comments AL-58 , I do my homework , decide what I need and go and get it , price is secondary when it comes to my top three

JR