ojmiddleton Posted February 19, 2015 Share Posted February 19, 2015 How easy is it to put a fatter rear tyre on an SR125? Is it just a case of putting one on or do I have to adjust other aspects also? Is there even room for a fatter tyre? Apologies for the lame question, but you guys have prooved do be most decent fellas :-) Link to comment Share on other sites More sharing options...
blackhat250 Posted February 19, 2015 Share Posted February 19, 2015 Whats on it O/J " , what happens is the wider tyre squeezed on to a narrower rim ,makes the tyre more pointed in the centre, Seen questions on other forums, folk trying to put 190s on a 5.1/5 inch rim [ designed for 180] and its steeper curve make it handle worse, 1 Link to comment Share on other sites More sharing options...
Moderator DirtyDT Posted February 20, 2015 Moderator Share Posted February 20, 2015 It depends on the size difference. It affects the handling, your insurance and - for the front tyre - the speedo readout. A fractional change isn't a major problem but keep an eye on the sidewall ratio (the 50, 55 90 bit of the spec) as this is the percentage of the width. A lot of classic riders have to compromise due to tyres being metric sizes now. Link to comment Share on other sites More sharing options...
AndrewElvisFan Posted February 20, 2015 Share Posted February 20, 2015 I'd also look at the cost of a non standard tyre - average for a half decent rear on an sr, including fitting is around £100 Link to comment Share on other sites More sharing options...
ojmiddleton Posted February 21, 2015 Author Share Posted February 21, 2015 Thanks guys , on the back is 3.50 16 4PR - was hoping to find out what these numbers refer to within the manual but no such luck So maybe best to get a wheel that could accomodate a wider tyre rather than squeeze one on the current rim? Link to comment Share on other sites More sharing options...
Moderator DirtyDT Posted February 21, 2015 Moderator Share Posted February 21, 2015 3.50 is inches wide. 16 is wheel rim diameter. 3.50 is 100/90 converted. 100/90 is 100mm wide and 90 is 90% of the width of the tyre; so 75mm (edit: the 75mm is wrong but corrected later in the thread) tyre wall height. I think that imperial and metric measure from different places on the tyre. Have a look here LINKY Link to comment Share on other sites More sharing options...
ojmiddleton Posted February 21, 2015 Author Share Posted February 21, 2015 Ok thanks very much DT! Link to comment Share on other sites More sharing options...
ojmiddleton Posted February 21, 2015 Author Share Posted February 21, 2015 keep an eye on the sidewall ratio (the 50, 55 90 bit of the spec) as this is the percentage of the width. A lot of classic riders have to compromise due to tyres being metric sizes now. Cluld you expand on the sidewall ratio point? Link to comment Share on other sites More sharing options...
Moderator DirtyDT Posted February 21, 2015 Moderator Share Posted February 21, 2015 if you had 100/100 tyre then the measurement width would be the same as the tyre wall measurement. As an easy example: If you have a 100/100 the tyre would be 100mm wide and 100% of the tyre width wall length -100mm wall. If you had a 100/90 the tyre would be 100mm wide and 90% of the tyre width wall length - 90mm wall. If you had a 100/80 the tyre would be 100mm wide and 80% of the tyre width wall length - 80mm wall. and so on. However; If you had a 120/90 the tyre would be 120mm wide and 90% of the tyre width wall length so 120 X 0.9 = 108mm wall. If you had a 120/80 the tyre would be 120mm wide and 80% of the tyre width wall length so 120 X 0.8 = 96mm wall Therefore: If the standard size tyre is a 100/100 and you put on a fatter 120/90 tyre the sidewall would be 8mm higher than standard (108mm - 100mm). If you put on a 120/80, the sidewall would be 4mm lower than standard 100mm - 96mm) If you you went for 120/100 because you thought it would only change the first 100 to 120 in the original spec, you would end up with a 120mm sidewall which is 20mm over standard!! In the front tyre this would alter the speed accuracy. On either tyre it would change the handling characteristics. 100/100 Remember the first part - in blue - is width size in mm. The second part - in red - is the percentage of the first part in mm. Will that do? Link to comment Share on other sites More sharing options...
ojmiddleton Posted February 21, 2015 Author Share Posted February 21, 2015 yes DT that is excellent thankyou, you really got stuck in!! :-) So are you saying that i need to keep my tyre width to tyre wall height ratio the same if i went for a fatter tyre? 3.50 = 100/90 would mean 100mm width and 90mm tyre wall height would it not? Not 75mm as in the quote below....3.50 is inches wide. 16 is wheel rim diameter. 3.50 is 100/90 converted. 100/90 is 100mm wide and 90 is 90% of the width of the tyre; so 75mm tyre wall height. LINKY Link to comment Share on other sites More sharing options...
Moderator DirtyDT Posted February 21, 2015 Moderator Share Posted February 21, 2015 yes DT that is excellent thankyou, you really got stuck in!! :-) So are you saying that i need to keep my tyre width to tyre wall height ratio the same if i went for a fatter tyre? 3.50 = 100/90 would mean 100mm width and 90mm tyre wall height would it not? Not 75mm as in the quote below.... Ooppps. yep 90mm. I am saying that if you pick a fatter tyre - and I don't recommend that - I would look for somthing with a very similar side wall height. I would stick to a a 100/90 TBH. Link to comment Share on other sites More sharing options...
ojmiddleton Posted February 22, 2015 Author Share Posted February 22, 2015 Thanks for the advice man, I think ill take it :-) i think im just gonna keep it standard and just wait for the bigger bike, cruiser style. I dont have the knowledge, ability or facilities to be messing about with stuff. The bikes great, if it aint broke....! Link to comment Share on other sites More sharing options...
Moderator DirtyDT Posted February 22, 2015 Moderator Share Posted February 22, 2015 Thanks for the advice man, I think ill take it :-) i think im just gonna keep it standard and just wait for the bigger bike, cruiser style. I dont have the knowledge, ability or facilities to be messing about with stuff. The bikes great, if it aint broke....! Got to agree. Plus you don't have additional hassle when insuring (Non standard size tyres). These company's spend millions of Yen on development; they should, and sometimes do, know best. Put the saved money into the "next bike" pot. 2 Link to comment Share on other sites More sharing options...
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