Hi all,
I was wondering if anyone knew the specs, or how to determine measurements for a fork. I am looking into replacements for my 85' 710, and there are a few Koga-Miyata forks on ebay right now. Thanks for the help.

You can find the fork offset by finding your bike in the appropriate brochure on the Vintage-Trek site. There will somewhere be an applicable goemetry spec giving the offset for 710s, but I can't say it will break out your size exactly. Trek in the old days was not consistent about that.

As far as blade length, maybe a current owner can measure the distance from axle center to brake bolt center.

After that it's steer tube length, and that is controlled by head tube length and headset stack height. Or see if someone with your size will measure it.

The 1985 Miyata catalog doesn't have the fork rake among the 710 specifications, so you'll have to obtain an undamaged fork and measure it. It's relatively easy to take the measurements off of a fork. This BikeCAD illustration shows the measurements taken from a 1987 Schwinn Paramount fork. The wheels are 700c.

R is the fork rake (40mm), and K is the axle center to brake brake bolt center (355mm). L is the length along the steering axis from the crown race to the axle center (365mm).

Haha,
Thank you Scooper, but if I could obtain an undamaged fork I wouldn't be in this pickle, lol. I guess I am looking for other 710 owners out there who happen to have my size as well. The forks on ebay right now are a Koga-Miyata Carboli, and an ALFREX alloy 6000. I dont have the tools to remove the fork so I would be heading to the LBS, but either of these two seems like good, if not much better, potential replacements. Is the head tube lenght a decent guage of how much steering tube I need in there?

https://www.ebay.com/itm/281134050412...84.m1438.l2649

https://www.ebay.com/itm/221257175190...84.m1438.l2649

Yes, the head tube length is a very good gauge of the steerer tube length required.

With a standard stack height threaded headset, the steerer should be 40 mm longer than the head tube. Taking my 62cm '87 Paramount as an example, using a Stronglight A9 headset, the head tube is 195 mm long, and the steerer from the crown race to the top is 235 mm.

EDIT - Looking at the '85 710 specs, the original fork is described as "Mangalight tubing with semi-sloping crown." I assume Mangalight is a manganese steel alloy, and personally I'd replace it with a steel one. I would not use an aluminum fork like the first one (item no. 281134050412).

Rats, I just did a quick measure with the calipers after unscrewing the stem nut and it looks like I will need about a 175mm steerer tube-so this takes both of those ebay forks out of the picture.

The Soma forks might match, but they are kinda pricey.