Does heat affect speedometers?

[Tom R]

I'm trying to figure out why my bike is faster in the morning (usually cool) than it is in the afternoon (it's been hot). At 5000 rpms, my speedo will read 80 or 81mph on the way to work, but sometimes as low as 72mph on the way home.
The clutch doesn't feel like it's slipping at any point - plus I've probably driven 600 miles with this disparity - so I think my clutch would have burned up by now if it was slipping.
Come to think of it, I guess it could just as easily be my tach acting up - could this be heat related?
I have 17/45 sprockets - so 80 mph should be about right at 5K rpms.

[5azzmonkey]

Tom,
Can you get someone to ride along side you and see if your if it's your speed or rpms that are changing?

[Tom R]

Tom,
Can you get someone to ride along side you and see if your if it's your speed or rpms that are changing?

Unlikey - as I'd have to get them coming and going. Maybe some sort of gps holder is in order.

[Tom R]

Well it's the tach. It seems to get more ambitious as the weather heats up. Speedo has been dead on with a gps I taped to the bars; but this morning I saw the tach get a little ambivalent between 4k and 5k - then it decided it was cool enough to be 4k.

[refeicul]

ive found a little change in how my speed to revs changes slightly with how aggressive or lac's i drive. like if i shift closer to red, or around like 5000rpm