Triumphrat

Apidae · 06-30-2004, 06:18 AM

Can anyone help? The last few of evenings I've been out hacking around the British country roads (N.Bucks) on the TT, I've experienced a strange "flat tyre" sensation. The bike just feels unstable and "squidgy". It only seems to last for a while but it's a bit unsettling. Ususally the bike feels totally solid and corners excellently.
I stopped and found no problem with the tyres. Tyre pressure is 36f/40r - no change before/after the ride. There's enough tred on the tyres and they appear in good condition.
The only thing I can imagine is that it's down to the road conditions. It seems to happen in the evening when the sun is low and the day is cooling off (OK, this is England - the day wasn't hot to begin with!). The roads appear dry but as they're narrow tree and hedge lined with grass verges, it may be that condensation is being pulled onto the road in a few places. Typical British roads are usually a bit rough but I don't think it's the bumps that are throwing the bike off.
A local friend of mine also experienced similar effect on his SV650.
Has anyone else had similar effect? I'm trying to simply ride through the effect and trust the bike as once the effect has worn off everything appears to be OK. I've only been riding the TT since May so it could be a local summer effect or my own inexperience on these roads. Otherwise, should I check chain, wheel alignment, bearings, ... ?

Will · 06-30-2004, 12:15 PM

Are your tires squared off a little? If they are, then there is a funny "break point" where you hit the ridge between the squared off point and the round part of the tire. That can make the bike feel like the back is about to step out a little. If you have a lot of miles on your tires, that might be it.

Apidae · 06-30-2004, 08:38 PM

The bike is currently fitted with BT010's. Total milage is 5130 (I bought it 1st May 2004 with 3130). I suspect the tyres are original from March 2001 but can't be sure.
Front tread depth is ~2.3mm centre and ~3.4mm edge; rear is ~2.4mm centre, ~4.5mm edge. The edge readings are at the edge of tyre wear (I've never pushed the tyres to the edge and the bike doesn't appear to have been taken on track days by previous owners).
Are these tread depths consistant with age/mileage/road use? Also, is there a specific place on the tyre to take a reading of tread depth?
I'm not used to assessing squareness of the tyres. Certainly the tyre feels slightly squared, but I would appreciate your comments based on the tread depths (if this helps).

Will · 06-30-2004, 09:00 PM

Tread depth doesn't matter as far as that odd handling feeling, except that the tread depths you describe tell that the tire is more worn in the middle than at the sides. When a tire wears, the worn center changes the geometry of the tire just enough that it feels odd when you are right at point it has been squared off. 5000 miles is not bad for BT010s. You can get a whole lot more miles than that if the tread depth is OK, but keep in mind that you will feel changes in handling as the tire's geometry changes due to wear.

Diego · 07-02-2004, 02:46 AM

I am not familiar with all sizes of that particular tyre for mileage (thank goodness they turn into tires once they reach this side of the Atlantic :-) ), but I agree with Will that the measurements do seem consistent with significant squaring.

That probably accounts for what you are feeling, and need not be a problem yet so long as you remain conscious of it. But there's one more thing you might want to check just to satisfy curiosity.

If you wet the tires and examine them from right angles, or if you just lightly move the palm of your hand over the tread, do you notice any cupping? Or perhaps a better description would be, a tendency for the leading edge of each tread block to be raised relative to the trailing edge of the block before it? The reason I ask is that the seeming sensitivity with particular road surface conditions sounds very much like what I experienced with a front tire (also a Bridgestone) that began failing prematurely with this type of wear. With the engineered grooving of modern tyres, if the leading edge of each tread segment/trailing edge of each groove doesn't contact the pavement at just the correct angle of attack each time, the handling magic goes away on some road surfaces, and "squidgy" is an apt description for the way it felt to me.

In my case, the handling on rough or grooved pavement deteriorated fairly rapidly, and I had to replace the tire at well under 4000 miles. I've had no repeat of that failure mode so far, but it's something one might watch for after a relatively few thousand miles.

07-02-2004, 04:46 PM

Does the unstable feel come from the front or back of the bike and at around what speeds? My nearly new tt feels light/unstable going through towns around 30mph, even my vespa handles better! Going round the countryside there are generally no problems unless i hit an overbanded white line. Also, as you stated you've only had you're tt for a month or so, are you getting used to the bike and now noticing things which were there initially but are now more noticable and you're getting more of a feel.
I think i would take it into a dealer and ask them to test ride..it may not even cost you anything as i do regularly.
Of course, it may be the tyres but i thought squaring off was due to extended periods of mileage on straightish roads/motorways. of which the tt isn't suited too, especially in the uk.

Apidae · 07-03-2004, 08:59 PM

Thanks for the comments. (In case of translation difficulties, for "tyre" please read "tire"! :wink: - I've got dual nationality UK/US but never learnt American spellings from my Mum (sorry, "Mom")):

Cupping of the tread - if you run your hand against the rotation of the tyre you feel a step up across the grooves. Therefore, if I imagine correctly, the edge that hits the tarmac first, is lower than the following edge. It's more noticeable on the front tyre and on the shorter length grooves. Is this consistent with a badly worn tyre, or is it designed so that both edges of the groove hit the tarmac at the same time (better seal and ejection of water?)?

Road surface/speed - the effect seems to occur on narrower country roads, which are often badly surfaced in the UK. Sounds similar to conditions experienced by Diego. Normally noticed at mid speed (40-60?) - although I didn't check the speed at the time!

Road use - although straight roads are rare in UK, I have ridden approx 700 motorway miles + some pillion miles (1-200). I don't know how the bike was ridden by previous owners, but this probably explains the squaring. I noticed the rear tyre appears unworn to 7/10th an inch from the edge. In normal road use, do you usually scuff edge-edge? (Perhaps I should push harder on the corners to keep the tyres in shape!?) Also, should I use another tyre better suited for touring use? (Personally, I think it's a great bike for sports/touring, although I would consider a double bubble if going for extended trips).

I first noticed the squidgy feeling from the front, although have also noticed the step out effect from squared rear once Will described it. I may, therefore, be experiencing a number of conditions. I'll ask the dealer for an opinion next time I'm near, but does anyone know if tyres can be scrubbed back to profile?
(I was hoping to keep this set until the next service).

Apidae · 07-12-2004, 07:40 AM

I asked a bike mechanic friend to advise on the tyres. He suggested the tyres were still OK but the rear suspension was a bit soft. I adjusted the rear suspension (now at 5-5 clicks - one firmer than standard). The bike seems far more stable on the corners. I couldn't get it to "squidge" over the weekend and found new cornering confidence ( :-D ) on the twisty country roads. I think as I gain more experience I'll be able to play around more with the suspension settings to get the bike perfectly setup for me. I also have an idea of what to look for on the tyres so I appreciate all your help and comments.