Tyre question

[JustNick]

Good evening all,

I've just purchased my first road bike and the front tyre feels like it is bottoming out going over bumps on the road both around town and on the open road. I weigh 100kgs am riding an FZR 250 and I'm pretty sure the tyres are Dunlop Arrowmax (GT501??) front and rear.

The tyre pressures are good at 33 psi front and rear (as per the manual). Should I be increasing tyre pressure? Looking to change tyres? Taking a closer look at my front suspension set up? Have I eaten too many pies to ride a 250??

[ajturbo]

i would get a new bike... lol

put a couple more of PSI in the rear for a start.. PM Shaun for more info on the set-up..:woohoo:

[frogfeaturesFZR]

34 f and 38 rear. How are your forks? Seals good, replaced the oil ?

[JustNick]

34 f and 38 rear. How are your forks? Seals good, replaced the oil ?

New bike so not sure and not sure. Do you think that would make a big difference? I was wondering if my forks might not be compressing properly and transferring the extra bumps onto the wheel.

[LBD]

New bike so not sure and not sure. Do you think that would make a big difference? I was wondering if my forks might not be compressing properly and transferring the extra bumps onto the wheel.

Put a cable tie around you forks and see how far it has moved when you experience the bottom out feeling...go from there

[JustNick]

Put a cable tie around you forks and see how far it has moved when you experience the bottom out feeling...go from there

Thanks for the tip, I'll give it a try tomorrow. Would it be adviseable to increase tyre pressures and see if that makes a difference? The general concensus from the threads I have read so far is it's not really a good idea on a 250 ...

[LBD]

Thanks for the tip, I'll give it a try tomorrow. Would it be adviseable to increase tyre pressures and see if that makes a difference? The general concensus from the threads I have read so far is it's not really a good idea on a 250 ...

Stick with the recomended tire pressures for now

[YellowDog]

In light of the problems you have experienced: With a 100Kg person on a small bike, I'd try 36 Front and 38 rear.

If they go 'POP', then "I'm sorry" :blink:

[FJRider]

I believe the problem is not a tyre issue ... more likely a suspension iussue ...

[4AGE]

I'm 90kg on a 250 and run 34 f and 36r. And this seems right for me.

Check to see if the fork seals are leaking?

[Hitcher]

The problem you're experiencing has nothing to do with your tyres. Put a replacement set on and fanny around with pressures relentlessly and you'll see that I'm right.

[JustNick]

Thanks for the helpful advice everyone, I'll start looking into the forks/suspension and let you all know how it goes.

[Robert Taylor]

Thanks for the helpful advice everyone, I'll start looking into the forks/suspension and let you all know how it goes.

It is a suspension problem, its both undersprung and underdamped even for a rider significantly lighter than you. If you raise the tyre pressures ( aside from taking away grip ) it will in fact make the suspension bottom out even more readily. That because the tyres are then doing less of the absorption duty and therefore placing more energy directly into the suspension.

[Gremlin]

New bike so not sure and not sure. Do you think that would make a big difference?
Absolutely. Suspension, like your engine, needs servicing, just not quite as regularly. Oil gets old, seals crack and so on.

Put a cable tie around you forks and see how far it has moved when you experience the bottom out feeling...go from there
Just tie it tight enough so that it doesn't move by itself (don't want it sliding down). Don't do it up as tight as you can, otherwise you'll damage the fork seals as they come in contact with the zip tie. The aim is that the tie shows how much of the fork leg you're using. It should be about 2/3.

[Robert Taylor]

Absolutely. Suspension, like your engine, needs servicing, just not quite as regularly. Oil gets old, seals crack and so on.

Just tie it tight enough so that it doesn't move by itself (don't want it sliding down). Don't do it up as tight as you can, otherwise you'll damage the fork seals as they come in contact with the zip tie. The aim is that the tie shows how much of the fork leg you're using. It should be about 2/3.

But just servicing it is not going to fix this problem

[JustNick]

It is a suspension problem, its both undersprung and underdamped even for a rider significantly lighter than you. If you raise the tyre pressures ( aside from taking away grip ) it will in fact make the suspension bottom out even more readily. That because the tyres are then doing less of the absorption duty and therefore placing more energy directly into the suspension.

You have a top reputation as a suspension specialist on here. What would your advice be? Given the symptoms is it likely that I could get any old motorcycle shop to look at it or would you recommend heading over to a specialist such as yourself or Shaun up in Auckland?

[Robert Taylor]

You have a top reputation as a suspension specialist on here. What would your advice be? Given the symptoms is it likely that I could get any old motorcycle shop to look at it or would you recommend heading over to a specialist such as yourself or Shaun up in Auckland?

Suspension has become a specialist job as the industry training for motorcycle mechanics has not kept pace with the times in respect of suspension. Thats a stark reality. It is clear that at minimum it needs firmer springs correctly preloaded and attention to oil viscosity. Ideally Race Tech emulators to sort out the remaining 50% of the problem, poor hydraulic control.

[JustNick]

Suspension has become a specialist job as the industry training for motorcycle mechanics has not kept pace with the times in respect of suspension. Thats a stark reality. It is clear that at minimum it needs firmer springs correctly preloaded and attention to oil viscosity. Ideally Race Tech emulators to sort out the remaining 50% of the problem, poor hydraulic control.

Thanks Rob, email sent.

[JustNick]

UPDATE: Well it turned out to be the front forks causing the problem in the end. I took them into the shop and had them disassembled and inspected and we found that they must have been leaking for a while as the oil levels and condition were low and poor, plus the forks had pitting in the travel area. So the forks were sent out of town for re-chroming and then reassembled with new seals and a heavier weight oil (the standard oil is about 7 weight from memory).

I just got the bike back today and put some kms on it and it feels like a completely different bike, no more bottoming out and I feel a lot more comfortable riding on the road again.

Many thanks to Steve from WOT Motorcycles Taupo - you were a big help mate and I'll definitely be paying you a visit in the future.

[LBD]

bingo...another happy camper

Enjoy the experience:scooter: