My bike has a 150/70R17 stock on the rear and a 120/70R17 on the front. It‘s getting close to the time to replace them. Although I can get an exact replacement in the same brand, I‘ve taking a liking to a tread pattern offered by a different manufacturer. Unfortunately, the closest size they offer is a 150/60R17. I know I should stick with a 150 to fit in the swingarm, but will the lower profile of the 60 ride noticeably different if paired with another 120/70 in the front? How much of a difference will it make in the actual speedo readings with a lower aspect ratio tire?
lower profile will affect top endbut not a lot.but then it will get there quicker. the only problem I can see is it may affect the steering geometry.your bike may ride better or worse.the only way to find out is do it see.
It's not a rocket ship where specs are critical, it's just a motorcycle. The rear tire change won't be noticeable. If you change the front tire specs, that would throw off the steering geometry a little (especially noticeable on a sport bike. Not so much on a cruiser).
Inspite of the fact that manufacturers give very specific tire sizes (IE 150/60/17 etc.) it has been my experience that one brands X/X/X size can be somewhat different than anothers X/X/X size. See if the dealer has both tires available on the rack and then stand them up to each other in order to judge the true difference. I suspect that the difference may be very small and probably un-noticable when driving. Regarding speedo reading changes it will make no difference if the speedo is driven off the front wheel. However, if your speedo drive is through the tranny you could put a tape measure around the tire before and after you change it and mathmatically calculate percentage of change.
