Tyre Questions

[Ricko19]

I know there have been a lot of threads on tyres and I have read a good many of them There have been some good recommendations re brands which I will be looking into, but I would still like to ask a couple of quick questions re tyre sizing and pressures:

Re transcribing the old tyre code values - My manual says my bike (GSX750ET 1980) should have the following tyre sizes:

Front : 3.25H19-4PR

Rear: 4.00H 18-4PR

You can get a width from this but how are you supposed to work out what profile you need?

my bike which I bought recently has the following mismatched tyres on it (and handles terribly) :

Front: Avon Super Venom 100/90 V19, DOT AT3F (W0200) date??

Rear: Pirelli Match MT08 130/80-18, DOT XEYD, X2AH, 3500

I'm not sure if these are the wrong sizes/profiles? I need to know what the correct size and profile is supposed to be? I was going to change the front at least because I think its dangerous the way it handles, but I gather if any of those numbers I quoted are the dates of manufacture, then I should probably replace both ASAP?

Also, the other threads have mentioned the recommended tyre pressures in your manual for the original fitment tyres(mine is 28F/32R) but I'm gathering that newer tryes need more pressure in them to perform properly? The last modern bike I had a few years ago used to run 36f and 42r, but I would have thought that this would be too high for these 'skinny' tyres that this bike takes?

I am just over 100kg, so would a good starting pressure be around 33psi front and rear, then use the hot/cold test?

This is the first older bike I will have had in a long time and the first I have had to replace tyres for. Any help appreciated

[sharpy]

Right tyre sizes i say. You could go smaller (90/90 and 120/80)on both and a smaller front would steer lighter, but personally ill stay that size. As for pressures ill be running 32/36 in them. But that me. And no-body say any crap about running them tubeless, THEY ARE NOT tubeless rims. Yes the 850's had a front tubeless but thats it.

[Nessism]

The 750 here in the states uses a 2.15" wide rear wheel so the max tire width for that size should be 120 if you value handling above looks.

So for your bike I recommend a 100/90 front and 120/90 rear (assuming the rear wheel width is the same as here). Both of these sizes are larger than the stock tires but they are tried and true on your bike.

[sharpy]

Opps didnt notice your a Qld boy. If thats the case give dave at Tyres for Bikes in Albion a call and pick his brain. I worked there for 17 yrs so im sure he is the right man to ask. 32624377 or http://www.tyres4bikes.com.au/

[Ricko19]

Thanks Sharpy - I'll give him a call during the week.

Thats Nessism Your post makes me even more confused with the widths though - I thought the 4.00 in the manual meant 4 inches accross, not 2.15" Man, I'm really confused

So is the 80 or 90 profile correct for the rear? And how can u tell from the old style measurements in the owner manual??

Hopefully Dave at TFB can enlighten me when I phone him Sharpy, but if anyone could explain it to me in the meantime, it would be much appreciated

[posplayr]

Not exactly sure but wheel size refers to the inside width of the rim. (e.g. 2.15")

The 4.00" is the outside width of the tire.

120mm tire fits a 2.15"x17" wheel (e.g. 120/90-17) using most of Ed's numbers

BTW I have a 130/80-18 on the stock wheel on my 81 GS750EX (virtually identical to your 80?) as well. It is close to the brake arm but fits and handles well enough. What makes a bigger difference is having nice round profile tires. I put Avons on and the bike actually moves side to side much easier than my ED now. I have Pirelli sportdemons on the ED and there are worn with a flat spot in the middle. That makes them harder to get into a turn.

There is no need or desire for me to dropping down to a 120/90-18.

Pos

[Nessism]

Tire and wheel width is something that comes up here all the time. Most people want the widest possible tire on their bike because they think it looks better. For a 2.15" wide rear wheel, a 120 is the max tire width that is generally recommended by the tire manufacturers. Regardless of what the experts say though, some people go wider than recommended...and live to tell about it. In the end, it's a personal choice. Using a tire wider than recommended will pinch in the sidewalls of the tire noticeably, and make the tread curve more tightly than designed. Again, most people don't seem to have serious problems with handling but my opinion is to let the tire people do what they do and our job is to listen and follow their lead unless we have compelling reasons not to.

[chef1366]

What is a Tyre?

[Ricko19]

Thanks guys Not interested in the widest tyres, just the right size ones for my rims. Am getting more sesible in my old age - hopefully!

Thanks for that Pos - that helps - will also stay away from the softer tyres I think.

Sorry Chef, forgot the US spelling - TIRES - happy?

Other normal English speaking people spell things as nature intended - tyre, colour ............